Battery charger with automatic voltage detection

ABSTRACT

A battery charger is disclosed that is configured to be connected to an external battery by way of external battery cables. In accordance with an important aspect of the invention, the battery charger is configured with automatic voltage detection which automatically determines the nominal voltage of the battery connected to its terminals and charges the battery as a function of the detected nominal voltage irrespective of the nominal voltage selected by a user. Various safeguards are built into the battery charger to avoid overcharging a battery. For battery chargers with user selectable nominal battery voltage charging modes, battery charger is configured to over-ride a user selected battery voltage mode if it detects that the battery connected to the battery charger terminals is different than the user selected charging mode.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a battery charger configured to beconnected to an external battery by way of external battery cables andmore particularly to a battery charger with automatic voltage detectionwhich automatically determines the nominal voltage of the batteryconnected to its terminals and charges the battery as a function of thedetected nominal voltage irrespective of the nominal voltage selected bya user.

2. Description of the Prior Art

Various battery chargers for charging different types of batteries areknown in the art. Examples of such battery chargers are disclosed inU.S. Pat. Nos. 5,729,115; 6,384,575; 6,625,477; and 7,468,596. Such abattery charger is also disclosed in US Patent Application PublicationNo. US 2007/0247105 A1, all hereby incorporated by reference.

Since each different type of battery needs to be charged according to aspecific charging algorithm for the specific battery, it is necessaryfor the battery charger to be properly configured for the battery typeand nominal voltage of the battery connected to its terminals. Someknown battery chargers require the user to determine the battery typeand nominal voltage of a battery connected to its terminals. Suchbattery chargers require the user to manually configure the batterycharger. Other known battery chargers automatically determine thebattery type and the nominal voltage of the battery connected to itsterminals and automatically configure the battery charger.

Various techniques are known for battery chargers for automaticallydetermining the nominal voltage of the battery connected to the batterycharger. For example, U.S. Pat. Nos. 6,384,575; 6,384,575 and US PatentApplication Publication No. US 2007/0247105 A1 all disclose batterychargers which distinguish different types of batteries by size. Ingeneral, these battery chargers include multiple charging pockets. Thepockets are configured to receive different size batteries withdifferent nominal voltages. These chargers merely need to sense whichpocket has a battery connected to it in order to determine the batteryvoltage. However, such a technique is not applicable to battery chargersthat are configured to be connected to external batteries by way ofexternal battery cables.

U.S. Pat. No. 6,625,477 discloses a different technique for determiningthe nominal voltage of a battery connected to its terminals. The batterycharger disclosed in the '477 patent is configured to identify thenominal voltage of specially configured batteries which include anidentification contact. The battery charger includes a plurality of tapvoltages juxtaposed so that when the battery is received in the batterycharger, the identification contact on the battery will be connected toa tap voltages depending on its size and thus nominal voltage. Again,such a technique is not applicable to battery chargers that areconfigured to be connected to external batteries by way of externalbattery cables.

U.S. Pat. No. 5,729,115 discloses yet another technique for determiningthe nominal voltage of a battery connected to its terminals. In thistechnique, the battery charger includes a sensing contact in addition tothe positive and negative battery terminals. The sensing contact isjuxtaposed adjacent to the positive battery charger terminal. Whenever abattery is inserted into the battery charger, the sensing contact isconfigured so that it will be in contact with the positive batteryterminal for a first type of battery and will not be in contact with thepositive battery terminal for a second type of battery. The batterycharger senses the voltage at the sensing contact and makes adetermination of the nominal voltage of the battery connected to itspositive and negative terminals based on the voltage at the sensingcontact. This technique, like the techniques discussed above, is notapplicable to battery chargers that are configured to be connected toexternal batteries by way of external battery cables.

Thus, there is a need for a battery charger that is configured to beconnected to an external battery by way of external battery cables thatcan automatically determine the nominal voltage of the battery connectedto its terminals.

SUMMARY OF THE INVENTION

Briefly, the present invention relates to battery charger configured tobe connected to an external battery by way of external battery cables.In accordance with an important aspect of the invention, the batterycharger is configured with automatic voltage detection whichautomatically determines the nominal voltage of the battery connected toits terminals and charges the battery as a function of the detectednominal voltage irrespective of the nominal voltage selected by a user.Various safeguards are built into the battery charger to avoidovercharging a battery. For battery chargers with user selectablenominal battery voltage charging modes, the battery charger isconfigured to over-ride a user selected battery voltage mode if itdetects that the battery connected to the battery charger terminals isdifferent than the user selected charging mode.

DESCRIPTION OF THE DRAWING

These and other advantages of the present invention will be readilyunderstood with reference to the following specification and attacheddrawing wherein:

FIG. 1 is a block diagram of a battery charger that is configured to beconnected to an external battery by way of external battery cables anddetermine the nominal voltage of a battery connected to its terminals.

FIGS. 2-7 are software flow diagrams for the battery charger illustratedin FIG. 1 for detecting the nominal voltage of the battery connected tothe terminals of the battery charger.

DETAILED DESCRIPTION

The present invention relates to a battery charger that is configured tobe connected to an external battery by way of external cables, such asbattery cables. In accordance with an important aspect of the invention,the battery charger is configured with automatic voltage detection whichautomatically determines the nominal voltage of the battery connected toits terminals and charges the battery as a function of the detectednominal voltage irrespective of the nominal voltage selected by a user.Various safeguards are built into the battery charger to avoidovercharging a battery. For battery chargers with user selectablenominal battery voltage charging modes, the battery charger isconfigured to over-ride a user selected battery voltage mode if itdetects that the battery connected to the battery charger terminals isdifferent than the user selected charging mode.

The present invention can be implemented on virtually any batterycharger, for example, the battery charger, illustrated in FIG. 1 andidentified with the reference numeral 10, disclosed in commonly ownedco-pending US Patent Application Publication No. 2005/0088144 A1, herebyincorporated by reference. The battery charger 10 includes amicroprocessor/microcontroller 12 and a pair of battery terminals ,generally identified with the reference numeral 17. Moreover, theprinciples of the present invention are applicable to any battery types,such as lead acid, absorbed glass mat (AGM), spiral wound AGM valveregulated lead acid (VRLA), flooded cell and deep—cycle batteries,generally identified by the reference numeral 16.

A battery charger is described and illustrated that is configured todetect whether a battery with a nominal 6 volts or 12 volts is connectedto its terminals. However, the principles of the invention areapplicable to detecting the nominal voltages of virtually any batteryconnected to the battery charger terminals. For example, the principlesof the invention can be used to determine the nominal voltages of 8, 24,36, 48, 60 volt batteries as well as the nominal voltage of virtuallyany battery. More particularly, the battery charger in accordance withthe present invention is able to determine the nominal voltage of anexternal battery connected to its terminals by taking certain voltagemeasurements under certain conditions. For batteries having nominalvoltages other than 6 volts/12 volts, the voltage levels set forth inFIGS. 2-7 are scalable. For example, for batteries with nominal voltagesother than 6 volt/12 volt, the voltage levels illustrated in FIGS. 2-7may be scaled in accordance with the ratio of the nominal voltages tothe 6 volt/12 volt voltage levels illustrated in FIGS. 2-7.

As used herein, the battery voltage measurement refers to the opencircuit battery voltage. In other words, the voltage across the batteryterminals with no current flowing from the battery charger through thebattery terminals. The principles of the present invention are alsoapplicable to closed circuit battery voltage measurements in which thebattery voltage measurements are made while an electrical current isflowing from the battery charger and through the battery terminals andthus includes the so called “IR” drop across the battery cables andbattery terminals.

Turning to FIG. 2, on power-up, the battery charger 10 initializes thesystem, as indicated by logic blocks 18 and 20. More specifically, theinput/output (I/O) ports on the microprocessor 12 are initialized alongwith the system clock. The analog to digital converters, which may beexternal or on board with the microprocessor 12, are calibrated and allsystem variables are initialized. In addition all LEDs are tested andset to their initial state. The variable “Initial Battery Check” isset=1 and the various timers as discussed below are initialized.

After initialization, the system proceeds to step 22 and checks thevoltage across its terminals 17. Specifically, the battery terminals 17are coupled to the ADC. The analog battery voltage is converted to adigital value and compared with a predetermined value. In other words,the system “reads” the voltage across the battery charger terminals anddetermines whether the voltage across the battery charger terminals isgreater than a nominal amount, for example, 0.2 volts DC, a value simplyindicative of whether a battery is connected across the batteryterminals. If there is no battery connected across the battery chargerterminals, the system loops back to steps 22 and 24 and waits for abattery to be connected to the battery charger terminals.

Once the system detects that a battery is connected across the batterycharger terminals 17, the system initially makes a simple voltagemeasurement in order to determine whether the battery connected to itsterminals has a nominal 6 volts or a nominal 12 volts. Morespecifically, the system initially determines in step 24 whether thevoltage across the battery charger terminals is greater than the nominalamount, illustrated in FIG. 2 as 0.2 volts DC. If so, the system assumesa battery of unknown nominal voltage is connected across its terminals.

For battery chargers equipped with user selectable mode switches, thesystem determines the position of the mode switch in step 28. Such modeswitches are used to initially select the charging algorithm to bedelivered by the battery charger to the battery connected to itsterminals 17. As described herein, the mode switch (not shown) is userselectable between 6 volts and 12 volts.

In step 26, the system measures the battery voltage and compares themeasured voltage with the voltage designated by the position of the modeselector switch to determine if the user selectable mode switch is setfor the correct mode. If the mode switch is set at 12 volts, the systeminitially determines if the measured voltage is less than 17 volts DC or8.5 volts DC if the mode switch is set in a 6 volt mode. If the measuredvoltage is greater than 17 volts DC, the system checks in step 28whether the user selectable mode switch was set for the 6 Volt mode. Ifthe measured voltage is greater than 8.5 volts DC the user selectablemode switch set for the 6 volts DC mode, the system assumes that a 12volt DC battery is connected to the battery charger terminal 17 In thiscase, the system over-rides the user selected position for the modeswitch and configures the system to charge battery in accordance withthe 12 volt algorithm, as set forth below, as indicated in step 30 andproceeds to step 32. In addition, the system optionally toggles one ormore LEDs indicating the over-ride of the user selected mode position instep 35. The system then loops back to the logic block 22 and repeatssteps 24 and 26. This time, since the battery mode was automatically setfor the 12 volt mode by the battery charger, the measured voltage willbe less than 17 volts and the system will proceed to step 34.

Alternatively, if the position of the user selected mode switch is setby the user to the 12 volt DC mode, the system checks in step 26 whetherthe voltage connected to its terminals 17 is less than 17 volts DC andgreater than 7.5 volts DC. the system assumes a 12 volt battery isconnected to the battery charger and proceeds to steps 34 and 32 andcharges the battery according to the 12 volt battery charger algorithm.

For battery chargers not equipped with a user selectable mode switch,steps 26, 28, 30 and 34 may be eliminated. In such a configuration, thesystem may be configured to proceed from step 24 directly to steps 34and 32.

Once a battery is connected across the battery charger terminals 17,each time the voltage across the battery charger terminals 17 ismeasured, the variable “Initial Battery Voltage” is incremented. Asindicated in step 20, the variable Initial Battery Voltage is initiallyset=1. For the first time the battery is connected across the batterycharger terminals or the charge has completed a desulfation charge, asindicated in FIG. 6, the system may optionally turn on an LED in step 34indicating that a battery is connected to its terminals. If the measuredvoltage in step 26 is greater than, for example, 7.5 volts DC, thesystem automatically assumes that the battery connected to its terminalsis a 12 volt battery in step 32 and charges the battery according to a12 volt charging algorithm, as will be discussed in detail below.

Alternatively, if the voltage measured in step 26 is less than, forexample, 7.5 volts DC, the system must determine whether the batteryconnected to its terminals is a depleted 12 volt battery or a 6 volt DCbattery. Accordingly, if the measured voltage is less than 7.5 volts DC,the system initially assumes that a 6 volt DC battery is attached to itsterminals, as indicated in step 36. In order to differentiate between adepleted 12 volt battery and a 6 volt battery when the measured voltageacross the battery charger terminals is less than 7.5 volts, a batterytest is conducted, as indicated by the logic block 38.

The test for determining whether the <7.5 volts measured in step 26represents a 6 volt battery or a depleted 12 volt battery is illustratedin FIG. 7. In particular, the test consists forcing a test current, forexample, 2-3 amperes DC, through the battery connected to its terminalsfor a short time, for example, 1 second, as indicated in step 40. Thepeak ripple voltage, i.e. closed circuit voltage, for example, acrossthe battery 16 is measured in step 42. If the peak ripple voltage isgreater than, for example, 11 volts DC, the system assumes the batteryconnected across the battery charger terminals is a depleted 12 voltbattery. In this situation, the system proceeds to steps 44 and 46 andinitiates charging of the battery in a 12 volt mode of operation.Alternatively, if the ripple voltage is less than 11 volts DC, thesystem proceeds to step 48 and initiates charging of the battery in a 6volt mode of operation.

Once the voltage of the battery connected to the battery terminals isdetermined, the system operates in various charging modes. FIGS. 3 and 4illustrate the 6 volt and 12 volt charging modes. FIG. 5 illustrates amaintenance charging mode. FIG. 6 illustrates a desulfation mode.

Referring first to FIGS. 3 and 4, even if the system determines that thebattery connected across its terminals is a 12 volt DC battery, thesystem includes various safeguards in a 12 volt charging mode in theremote chance that the battery determined by the system to be a 12 voltbattery is actually a 6 volt DC battery. In particular, in a 12 volt DCcharging mode, the duty cycle of the charging current is set to aminimum, for example 25% in step 50 (FIG. 2). Optional Charging LEDs arealso turned on. Once the duty cycle of the charging current isminimized, charging is started, as indicated by the logic block 52(FIGS. 1 and 2). For the initial period of the charge in both a 12 voltDC charging mode and a 6 volt DC charging mode, for example, the first 2minutes, as indicated in step 54, the system determines whether thebattery connected to its terminals suffers from a condition commonlyknown as sulfation.

Sulfation is a condition associated with lead acid batteries. Thiscondition occurs when a lead-acid battery loses its ability to hold acharge after it is kept in a discharged state too long due to thecrystallization of lead sulfate within the battery. The desulfation modeis discussed below.

In both a 6 volt charging mode and a 12 volt charging mode, after thefirst charging period, the charging current is limited, for example, toa nominal amount, for example, 1.5 amps DC, as indicated in step 56. Thesystem repeatedly measures the voltage of the battery connected acrossits terminals 17. When the voltage exceeds 9 volts in a 12 volt chargingmode, for example, as indicated by the logic block 58, the systemassumes that the battery connected to its terminals is a 12 volt batteryand proceeds with a normal 12 volt charge with safeguards as discussedherein. In a 6 volt charging mode, if the battery voltage exceeds 4.5volts, the system proceeds with a normal 6 volt charge.

In both the 6 volt mode and the 12 volt mode, the battery is chargeduntil the time out period runs, for example, 2 hours, or the batteryvoltage exceeds 12 volts DC in a 12 volt mode or exceeds 6 volts in a 6volt mode, as indicated by the logic block 60 (FIG. 3). The time outperiod functions as a safety check to make sure that the battery voltageincreases to at least 4.5/9.0 volts in a 6/12 volt mode in for example,2 hours.

During the charging period, the system continually checks whether thevoltage of the battery connected to its terminals 17 is Vmax, Vmaxrepresents the previously measured highest voltage of the battery. Thesystem repeatedly checks the voltage of the battery in step 62 andwhether the 2 hour timer has timed out in step 64.

If the battery charger was initially configured for a 6 volt operatingmode, and the battery voltage exceeds, for example 9.5 volts DC, asindicated in step 70, the system proceeds to step 72 and charges thebattery in a 12 volt charging mode. During conditions in which thebattery voltage is <9.5 volts and the system is configured in a 6 voltDC charging mode, as indicated by the logic block 70, the system assumesa 6 volt charging mode. During a 6 volt charging mode, the systemregulates the battery voltage at Vmax, i.e. the previously measuredhighest DC voltage in step 84. The system also continues to regulate therate of change of charging current, for example, at a constant current,i.e. dl/dt=0, for example 1.5 amps During a 6 volt charging mode, theduty cycle of charging current is repeatedly monitored, as indicated bythe exemplary logic illustrated in block 86, where the symbol IIrepresents a logical OR. In general, the voltage is held constant atVmax by continuously reducing the current by reducing the duty cycle.Once the current levels off and the voltage is maintained, the systemassumes that the battery is fully charged, Once the battery is fullycharged, the system enters a maintenance state, as indicated by thelogic block 88.

If the battery voltage is less than 9.0 volts, for example, for thefirst 60 minutes of charging, as indicated by the logic blocks 58 and 76(FIG. 3), the system determines whether the current battery voltageexceeds 6.5 volts in step 78. If the battery voltage exceeds, forexample, 6.5 volts, a further safeguard is provided by the system toprevent accidental charging of a 6 volt battery during a 12 voltcharging mode. In particular, the rate of change of the charging currentdl/dt is limited, as indicated by the logic block 80. In particular thecharging current is regulated at a constant value, for example, 1.5amps, i.e. dl/dt=0.

In a 12 volt mode, if after 60 minutes, the voltage across the batterycharger terminals is <6.5, as indicated by the logic block 78, thebattery is assumed to be damaged and the charge is terminated, asindicated by the logic block 82.

Once the 2 hours have passed, the system checks in step 66 whether thecurrent battery voltage is greater than the initial battery voltage. Ifso, the initial battery voltage is set to equal the current batteryvoltage in step 68 and system loops back to steps 62, 64 66 and 68 untilthe battery voltage exceeds Vmax, as indicated by the logic block 62. Inaddition, after the 2 hours have passed, if the system determines thatthe current battery voltage is not greater than the initial batteryvoltage, the system assumes a lack of progress in step 67. During thiscondition the battery voltage is measured. If the voltage is greaterthan, for example 12.8 volts DC, as determined in step, the system setsVmax=the current battery voltage in step 71. The system loops back tostep 60 and continues to charge. Alternatively, if the voltage measuredin step 69 is less than 12.8 volts, the battery is assumed to be damagedand charging is terminated, as indicated in step 73.

The maintenance charge mode is illustrated in FIG. 5. Initially in steps90 and 92, the charging LED is turned off and the maintenance charge LEDfor a predetermined time period, for example, 60 seconds. After thepredetermined time period, the system checks whether the battery voltageVbat<the maintenance charge voltage Vmaint, for example, 12.8 volts DCin a 12 volt charging mode and 6.4 volts DC in a 6 volt charging mode.If the battery voltage Vbat<the maintenance charge voltage Vmaint, thesystem and continuously loops back to step 90 and maintains themaintenance charge LEDs on until the battery is disconnected.Alternatively, if the voltage Vbat>the maintenance charge voltageVmaint, the system is configured in order to regulate the batteryvoltage at the maintenance voltage Vmaint, as indicated in step 96. Inother words, a maintenance charging current is pumped into the batteryin order to regulate the battery voltage at the maintenance voltageVmaint. Next, in step 98, the system checks whether the battery voltageVbat has climbed above the maintenance voltage Vmaint, by a nominalamount, for example, 0.1 volts DC. If so, the system maintains themaintenance charge LEDs on and continues regulating the battery voltageat the maintenance charge voltage Vmaint. If the battery voltage Vbat isnot greater than the maintenance voltage by a nominal amount, the systemwill attempt to maintain the battery at 13.2 volts DC in a 12 volt modeand 6.6 volts DC in a 6 volt mode with up to a nominal maintenancecharging current, for example, up to 500 mAmps, as indicated in step100. During a maintenance charge mode, the system repeatedly checks thebattery voltage. If the battery voltage in a 12 volt mode drops below,for example, 12.8 volts in a 12 volt mode or 6.4 volts in a 6 volt mode,as indicated in step 102, the system initiates a full 12 volt or 6 voltcharge in step 104. If the battery voltage is >12.8 volts in a 12 voltmode or > than 6.4 volts in a 6 volt mode, the system stays in amaintenance charge mode and repeats steps 94-102.

As mentioned previously, a sulfation condition is a condition of leadacid batteries that will not hold a charge due to the crystallization oflead sulfate. Desulfation is a process of repeatedly sending shortcurrent surges through the damaged battery. The current pulses tend tobreak down and dissolve the sulfate crystals, restoring some of thebattery's capacity over time.

Turning first to FIG. 3, during the first portion of every chargingcycle of lead acid batteries, the system checks for a sulfationcondition. In particular, the system checks the initial voltage of thebattery and then ramps up the charging current from a minimum to, forexample 1 amp, in step 104 and checks the peak battery voltage in step106. If the peak voltage is >11 volts, for example, but the initialvoltage was less than 3 volts, for example, the system assumes asulfation condition exists and initiates a desulfation charge asindicated by the logic block 108.

A 6V and 12V sulfated battery look about the same. In general, thecharger 10 will try to maintain the battery voltage at around 15.4V witha current with a relatively low maximum. If the battery is salvageable,the current will hit the maximum and the voltage will begin to driftdown. If it drifts down below, for example, 11V, then the battery ismost likely a 6V battery. Rerunning the battery detection test mentionedabove can be used to confirm the determination. More specifically, thedesulfation charge mode is illustrated in FIG. 6. In a desulfationcharge mode, desulfation LEDS are flashed in step 110. The desulfationcharge is conducted for a set time period, 8 hours, for example, asindicated by the logic block 112. After the set time period, thedesulfation charge is terminated, as indicated by the logic block 114.During the desulfation charging period, the battery voltage is regulatedat, for example, 15.4 volts, as indicated by the logic block 116. by wayof current pulses are applied to the battery. The current pulses areapplied to the battery until the battery accepts charge.

During a desulfation mode, the battery charger is actually maintainingthe peak ripple voltage at the high voltage. The actual battery voltagewhen the charger is off during this period is generally unreliable as anindicator of battery health from 0.1V on up. The system determines ifthe battery has been recovered and can accept charge if the batterybegins to take current, i.e. the charging duty cycle has increased to asufficient level or if the peak ripple has come down substantiallybelow, for example 11 volts. Once the system determines that the batteryhas recovered, y the battery is initially charged in a 6 volt mode, asindicated by the logic box 120. The nominal voltage of the battery issubsequently determined, as discussed above and the battery is chargedas a function of its nominal voltage.

Obviously, many modifications and variations of the present inventionare possible in light of the above teachings. Thus, it is to beunderstood that, within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described above.

1. A battery charger comprising: a pair of battery terminals; ameasuring system for measuring the voltage of a battery connected acrosssaid battery terminals; a determining system for automaticallydetermining the nominal voltage of the battery connected across thebattery terminals; and a charging system for automatically charging thebattery as a function of the nominal voltage determined by saiddetermining system.